A kinetic energy penetrator is a type of ammunition which, like a bullet, does not contain explosives and instead uses kinetic energy to penetrate the particular target. A kinetic energy penetrator is typically a high-density object with a high aspect ratio, which penetrates solid bodies by means of its own momentum. Typically, a kinetic energy penetrator is in the form of a rod which may be flat, pointed, or rounded at one end.
The principle of the kinetic energy penetrator is that it uses its kinetic energy, which is a function of mass and velocity, to penetrate armor. Modern kinetic energy penetrators maximize kinetic energy and minimize the area over which it is delivered by being fired with a very high muzzle velocity, concentrating the force in a small impact area while still retaining a relatively large mass, and maximizing the mass of whatever volume is occupied by the projectile by using the densest metals practical.
It is desirable for kinetic energy penetrators to have a large amount of remaining kinetic energy at impact. Remaining kinetic energy is directly proportional to velocity and mass of the penetrator at impact. Depleted uranium-based alloys have conventionally been used in kinetic energy penetrators due to their high-density of approximately 19 grams/cm3 in order to carry the required mass at penetration.
It is also desirable for kinetic energy penetrators to have very little widening of the penetrators' cross section during impact and penetration. The undesirable widening effect is sometimes referred to as “mushrooming.” It is believed that a penetrator that has little mushrooming on impact will travel more efficiently into and through the target. Kinetic energy penetrators made of depleted uranium typically have very little mushrooming due to what is believed to be an adiabatic shearing mechanism of the material. Adiabatic shearing promotes a self-sharpening mechanism that provides a longer penetration time in the target than a material without this property.
Despite its desirable performance properties, depleted uranium and its alloys have many significant manufacturing and environmental hazards associated with its use. For example, depleted uranium alloys are costly to fabricate, handle, and store because of their extremely complex metallurgy and the obvious health considerations associated with the use of uranium.
A variety of tungsten heavy alloy based penetrators have been developed as a substitute for depleted uranium. However, these materials require significantly higher initial impact velocity to penetrate a target when compared to depleted uranium. Moreover, materials such as tungsten do not demonstrate adiabatic shearing during impact and penetration but instead demonstrate significant mushrooming. Tungsten carbide-cobalt alloys have also been used in kinetic energy penetrators, however, these materials have comparatively low densities and a relatively high rate of shattering on impact.
Typical powder metallurgy processes using, for example, either depleted uranium or tungsten-based materials, include a step where the powder form is subjected to very high temperatures to allow the powder particles to sinter, either through a solid-state process or, if a secondary binder is present that reaches a liquid state, through liquid phase sintering. Both of these processes enable secondary effects, such as grain growth during the high temperature portions of the process. This grain growth occurs quite rapidly and can mean that the final consolidated material will have a grain structure that is significantly different from the initial grain structure in the powder. In the case of the initial powder state containing grains sized in the nanometer scale, these grain growth mechanisms can be triggered at lower energy levels due to the highly reactive and high surface area nature of these particles. Thus, it has typically been difficult to maintain a nanometer sized particle after sintering.
One method to control grain growth in typical sintering practice is to include additives to the base powder that act as barriers to the grain growth process. An example of this is the addition of tantalum to tungsten carbide-cobalt powders where the tantalum, usually in the form of tantalum carbide, forms on the grain boundaries of the tungsten carbide grains and prevents the overall grain growth mechanism.
Therefore, it would be desirable to have a material for use in a kinetic energy penetrator that approaches the density of depleted uranium so as to have a large amount of remaining kinetic energy at impact, maintains nanometer-scale particles, and undergoes adiabatic shearing so as to exhibit very little mushrooming on impact allowing more efficient penetration into the target.
The present invention has been developed in view of the foregoing.